A brief description will be given below of contents of a downlink control channel in an IEEE 802.16m system. Downlink control channels include indispensable information required for operating the IEEE 802.16m system. Information transferred over the downlink control channel is hierarchically transmitted on different time scales from a superframe level to an Advanced Air Interface (AAI) subframe level.
A Super Frame Header (SFH) serving as one of downlink control channels includes necessary system parameters and system configuration information, and is then transmitted to a destination. In particular, the SFH includes system information needed for an advanced mobile station (AMS) to perform initial network entry, network re-entry, or handover. The SFH includes a Primary Superframe Header (P-SFH) and a Secondary Superframe Header (S-SFH). The P-SFH may be transmitted every superframe. The S-SFH may also be transmitted every superframe. The SFH may also be called a broadcast channel (BCH) (wherein the BCH may be classified into a primary broadcast channel (P-BCH) or a secondary broadcast channel (S-BCH)), or may have the same meaning as the BCH.
An Advanced MAP (A-MAP) includes unicast service control information. Accordingly, the A-MAP may also be called unicast control information. The unicast service control information may be mainly classified into user specific control information and non-user specific control information. The user-specific control information may be classified into assignment information, HARQ feedback information, and power control information. The assignment information is transmitted to an assignment A-MAP, the HARQ feedback information is transmitted to an HARQ feedback A-MAP, and the power control information is transmitted to a power control A-MAP.
FIG. 1 shows an example of a location to which an A-MAP area is allocated in a Time Division Duplex (TDD) frame structure of a mobile communication system.
Referring to FIG. 1(a), one frame includes 8 subframes. In this case, an A-MAP transmission period (or A-MAP allocation period) may be denoted by 1 (n=1) or 2 (n=2). Referring to FIG. 1(b), it can be recognized that one frame includes 7 subframes. Likewise, the A-MAP transmission period may be denoted by 1 or 2. In this way, one frame may include 7 or 8 subframes. In the frame structure in which one frame includes 7 or 8 subframes, the A-MAP may be transmitted to the mobile station during the transmission period of 1 or 2. In this case, the A-MAP transmission period means a specific period in which the A-MAP is assigned to each subframe and transmitted. If the A-MAP transmission period is denoted by 1, this means that the A-MAP is assigned to each subframe of one frame composed of 7 or 8 subframes and is transmitted to the mobile station. If the A-MAP transmission period is denoted by 2, this means that A-MAP is assigned to every two subframes of one frame composed of 7 or 8 subframes, and is transmitted to the mobile station.
Generally, one frame having a channel bandwidth of 5 MHz, 10 MHz, or 20 MHz includes 8 subframes, and one frame having a channel bandwidth of 8.75 MHz includes 7 subframes. There is one limitation to the A-MAP transmission. Specifically, it is necessary for at least one A-MAP to be transmitted at a first subframe every frame. In the TDD frame structure shown in FIG. 1(a) or 1(b), the number of subframes belonging to one frame and the A-MAP transmission period has little effect upon the system performance and flexibility.
FIG. 2 shows an example of a location to which an A-MAP area is allocated in a
Frequency Division Duplex (FDD) frame structure of a mobile communication system.
In the FDD frame structure shown in FIG. 2 in the same manner as in FIG. 1, one frame may include 7 or 8 subframes according to a channel bandwidth. In other words, one frame having a channel bandwidth of 5 MHz, 10 MHz, or 20 MHz may include 8 subframes, and one frame having a channel bandwidth of 8.75 MHz includes 7 subframes. In the FDD frame structure shown in FIG. 2, there is a limitation to the A-MAP transmission. In other words, at least one A-MAP is allocated to a first subframe every frame.
Referring to FIG. 2(a), one frame may include 8 subframes. The A-MAP may be allocated to one frame (i.e., 1 transmission period) or two subframes (2 transmission periods), and may be allocated to the mobile station. If the A-MAP transmission period is denoted by 2 in the FDD frame structure in which one frame includes 8 subframes, the A-MAP transmission period of 2 has little effect upon system performance.
Referring to FIG. 2(b), one frame may include 7 subframes. The A-MAP may be allocated to one frame (i.e., 1 transmission period) or two subframes (2 transmission periods), and may be allocated to the mobile station. If the A-MAP transmission period is denoted by 2 in the FDD frame structure in which one frame includes 8 subframes, the A-MAP transmission period of 2 has little effect upon system performance. However, provided that the A-MAP transmission period is denoted by 2 in the FDD frame structure in which one frame includes 7 subframes, and the A-MAP allocation is conducted to satisfy the limitations of the A-MAP transmission, the last subframe area 210 of a first subframe neighbors a first subframe area 220 of a second frame.
The A-MAP is allocated to each of two neighboring subframes 210 and 220, such that the system unavoidably generates unnecessary overhead in such control signaling, resulting in deterioration of system performance (e.g., throughput) and flexibility. As a result, there is needed a solution for preventing the system performance and flexibility from being deteriorated.